The present invention relates to a plasma processing method which comprises carrying out etching of samples and cleaning of inner wall of vacuum vessels with plasma.
In the field of production of semiconductor devices, nonvolatile materials are being used as materials to be etched for FRAM (Ferroelectric Random Access Memory) or MRAM (Magnetic Random Access Memory) in addition to materials such as Si, Al and SiO2 which have been used as materials to be etched for DRAM (Dynamic Random Access Memory) or LOGIC. The nonvolatile materials are difficult to etch because reaction products at the time of etching are high in melting point. Furthermore, since reaction products after etching are low in vapor pressure and high in coefficient of adhesion to inner wall of vacuum vessels, when several to several hundred samples are processed, the inner wall of the vacuum vessels is covered with deposits, which peel off later to cause formation of many foreign matters. Moreover, the coupling state of an induction antenna and plasma in the reaction vessel is changed by the deposits to cause change with time of etching speed or uniformity, verticality of etching, and state of adhering of side wall to the etched side wall. As examples of the nonvolatile materials, mention may be made of ferromagnetic materials or antiferromagnetic materials used for MRAM or magnetic heads, such as Fe, NiFe, PtMn and IrMn, noble metal materials used for capacitor part or gate part of DRAM, capacitor part of FRAM or element part of TMR (Tunneling Magneto Resistive) of MRAM, such as Pt, Ir, Au, Ta, Ru, and, besides, high dielectric materials such as Al2O3, HfO3 and Ta2O3, ferroelectric materials such as PZT (lead titanate zirconate), BST (barium strontium titanate) and SBT (strontium bismuth tantalate).
As one of conventional plasma processing methods and processing apparatuses, there has been an induction type plasma processing apparatus using a coil-shaped antenna provided at outer periphery of a vacuum vessel or a plasma processing apparatus into which a microwave is introduced. In both the apparatuses, the countermeasure against deposits on the inner wall of the vacuum vessel in etching of nonvolatile materials is not sufficient, and, hence, cleaning with atmospheric exposure has been repeatedly carried out. When cleaning is carried out once, 6-12 hours are required before starting of next processing of the sample to cause deterioration of working efficiency of the apparatuses.
On the other hand, there has been proposed an apparatus according to which a Faraday shield is provided between antenna and plasma and electric power is supplied by connecting a high-frequency electric source to the Faraday shield, whereby deposition of reaction products on the inner wall of vacuum vessel is inhibited and cleaning of the inner wall of the vacuum vessel can be performed. As examples thereof, there are techniques disclosed in JP-A-10-275694 and JP-A-2000-323298.